[IPV6] NDISC: Add proxy_ndp sysctl.

We do not always need proxy NDP functionality even we
enable forwarding.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 1d6d3cc..caca57d 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -176,6 +176,7 @@
 	__s32		accept_ra_rt_info_max_plen;
 #endif
 #endif
+	__s32		proxy_ndp;
 	void		*sysctl;
 };
 
@@ -203,6 +204,7 @@
 	DEVCONF_ACCEPT_RA_RTR_PREF,
 	DEVCONF_RTR_PROBE_INTERVAL,
 	DEVCONF_ACCEPT_RA_RT_INFO_MAX_PLEN,
+	DEVCONF_PROXY_NDP,
 	DEVCONF_MAX
 };